I know there have been threads on which books to learn DG/RG from but hopefully this is sufficiently different to avoid closure.
Can anyone recommend a book to learn DG/RG (whichever is appropriate) so that I can do PDEs on manifolds? At the moment I am reading through John M Lee's Introduction to Smooth Manifolds and I am wondering whether I really need to learn all the topics in it since it doesn't touch RG which I believe is more used in the theory of PDEs. Maybe there is a better text.
Also, any topics to particularly study or avoid would be useful.